1. Field of the Invention
The present invention is directed to thermal imaging systems, and is more particularly directed to an electronic zoom for use in a Signal Processing in the Element (SPRITE) infrared imaging system.
2. Description of Related Art
Scanning thermal imaging systems are used in a variety of applications, including surveillance systems and target detection/recognition systems. Such systems typically incorporate a telescopic lens assembly coupled to a scanner. The scanner scans energy from a scene through an imager lens assembly onto a detector array having a plurality of photoelectrically responsive detector elements perpendicular to the scan direction. Each of these detector elements provides an electric signal proportional to the flux of infrared light on the particular detector element. Electric signals generated from the detector elements are subsequently processed by system sensor electronics to create an image for display on a system output device.
Resolution of an imaging system is influenced by the pixel size of the display Cathode Ray Tube (CRT) (i.e., spot size), and by the viewer's visual acuity. In order to increase resolution, zoom features are incorporated which allow an operator to realize the full resolution capability of the basic system. This enables the operator to detect targets at a greater range and to observe features that enable determination of target type.
Prior to the present invention, zoom capabilities were provided by optical configurations. However, for a high range of zoom ratio, the equipment necessary for an optical zoom becomes bulky and expensive. While electronic zoom configurations have been used in other imaging systems to extend the zoom range without incurring significant cost or size penalty, the electronic zoom has not been successfully implemented in a Signal Processing in the Element (SPRITE) detector based system. This is due to the difficulties imposed by the scanning technique of a SPRITE based system.
The difficulties of a SPRITE based system stem from the fact that a given line is not generated by the same SPRITE element on every field. Furthermore, the method of using an eight detector SPRITE configuration to obtain improved signal-to-noise performance, creates additional complications for use of an electronic zoom.
Therefore, it is the object of the present invention to provide a system and methodology for providing a zoom capability in a SPRITE infrared imaging system which addresses the above-described difficulties. The present invention establishes a novel sequence for reading data out of a scan converter to make an electronic zoom feasible as a separate mode of operation in a system which utilizes SPRITE detectors.